Two big steps forward for quantum teleportation

Few things will tie your cerebral lobes in a knot like quantum mechanics, and even then, fewer things are as astonishing as quantum teleportation – the “transmission” of quantum values (qubits) over a distance – not feet but hundreds of kilometers (or miles). The research into this potential form of communication has been going on for a couple of decades, and advances seem to come with some regularity. (Two SciTechStory articles, one from 2010 and the next from 2012 chronicle this.)

[SciTechStory: Quantum teleportation over 16 km in open air]
[SciTechStory: Quantum Teleportation: Step 4, 150 Kilometers 1280]

In its simplest form, quantum teleportation is grounded in the quantum mechanics of photons (the electrons of light) that have entanglement, the quantum state where the behavior of one photon is inextricably bound to another photon. In quantum teleportation, a maximally entangled pair of qubits are created (using laser light), one qubit (a) of the pair is retained at the sender point (traditionally called Alice) and the other qubit (b) sent to a receiver point (called Bob). In order to communicate, the first step is to combine Alice’s qubit, a, with an ‘information’ qubit, c = ac. This produces two classical bits, the same bits as a computer, an electronic on/off state. The process destroys the ac qubit. Because a and b are entangled, the qubit at Bob is now the qubit bc, however the state (or value) of bc is indeterminate (could be any one of four states). So Alice sends by traditional communication (wire, laser, broadcast) the two classical bits, which are applied to bc converting it into an identical recreation of c. Now Bob has the information qubit c.

The most recent work, conducted by Professor Akira Furusawa and his team at the University of Tokyo (Japan) and assisted by Professor Peter van Loock of Johannes Gutenberg University (Mainz, Germany), published in the journal Nature [14 August 2013, paywalled, Deterministic quantum teleportation of photonic quantum bits by a hybrid technique], achieved quantum teleportation of a ‘field’ of photonic qubits. Previous experiments involved entanglement of only two photons. This experiment succeeded in simultaneous entanglement of many photons, which the researchers were able to control (on and off) and transmit by teleportation (in this case four qubits at a time).

In effect, the Tokyo experiments created a quantum teleportation channel, complete with error correction qubit and the ability to generate and read quantum information from fields of entangled photons. The uniqueness of this experiment, in essence the ability to deal with multiple entangled photons and many qubits at a time, represents an advance in the development of quantum communication.

This research was matched by development in Switzerland of a specialized chip that for the first time allows the measurement of photonic qubits without destroying them. Andreas Wallraff and his team at the Quantum Device Lab at the Swiss Federal Institute of Technology (Zurich, Switzerland) developed a ‘superconducting circuit architecture’ (a microchip) that allows input of quantum information into one circuit, which causes the signal going to a second circuit to alter its quantum state and in turn, use that altered signal to determine the properties of the original information and transfer it to the second circuit. This is, in a sense, a signal processor for quantum teleportation.

The details of the Tokyo and Swiss research, although published in the journal Nature, are buried (or withheld) in proprietary description, so a completely non-jargon explanation of the techniques involved is not available. Suffice it to say, that these two developments are major steps forward for quantum teleportation, and quantum teleportation techniques are the basis of quantum communications and quantum computing. It is hard to underestimate the impact of these two quantum technologies, although they won’t become ‘visible’ in applications for many years, if not decades. Even the distinctiveness of these two tracks of experimentation reveals how much work remains to be done before some kind of standardized and consolidated technology of quantum teleportation emerges.

Research Spectrum

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